The major objectives of this research proposal is to elucidate the mechanism of control of serum albumin biosynthesis and secretion, a useful model for understanding the regulation of protein biosynthesis associated with secretion. The role of proalbumin, a novel intracellular precursor to serum albumin in normal rat liver will be studied. Subcellular fractions catalyzing the synthesis of the precursor and its subsequent efficient conversion to finished albumin will be obtained from liver extracts. The mechanism of the latter reaction, its requirements and kinetics, will be studied. The activity of this enzymatic conversion system will be compared with the rate of biosynthesis of albumin precursor under a variety of situations known to markedly affect serum albumin secretion in vivo: these include dietary protein depletion, and experimentally induced nephrosis.